We report here the isolation of a novel hydroxylated pyrrolidine derivative from the seeds of the legume Castanospermum australe A. Cunn., the same source of the β-glucosidase inhibitor 1,6,7,8-tetrahydroxyoctahydroindolizine (castanospermine). The alkaloid was isolated as a crystalline hydrochloride, with its composition shown to be C₅H₁₂ClNO₂ by elemental analysis and mass spectrometry (the protonated amine was detected at m/z 118 in the chemical ionisation mass spectrum). The structure was established as 2-hydroxymethyl-3-hydroxypyrrolidine hydrochloride (1) using ¹³C and ¹H NMR spectra (for a D₂O solution). The 300 MHz ¹H spectrum contained multiplets for eight protons (including three geminally coupled CH₂ groups), with the lowest field signal (δ 4.24) assigned to the C-3 proton; spin-decoupling revealed its adjacency to a CH₂ group (δ 2.13, 1.90) and another proton (δ 3.47), and complete multiplet analysis was achieved via spin simulation. The electron impact mass spectrum supported the structure, showing a weak molecular ion for the free amine and an intense ion at m/z 86 from loss of CH₂OH. Relative and absolute configurations were determined by X-ray crystallography: C₅H₁₂ClNO₂ crystallizes in the tetragonal space group P4₁2₁2 (a = 9.940(3) Å, c = 14.822(2) Å, U = 1464.59 ų, Dc = 1.393 g cm⁻³, Z = 8, F(000) = 656, μ(Mo-Kα) = 4.54 cm⁻¹). The chloride ion occupies two independent positions to maximize hydrogen bonding: O(1)-H(11)...Cl(1) and O(2)-H(12)...O(1) bonds form sheets perpendicular to c, linked by N(1)-H(2)...Cl(2) bonds. Compound (1) was identified as (2R,3S)-2-hydroxymethyl-3-hydroxypyrrolidine hydrochloride. Other natural hydroxylated pyrrolidine derivatives (excluding amino acids) include 2,5-dideoxy-2,5-imino-D-mannitol (from Derris elliptica leaves) and 2-hydroxymethyl-3,4-dihydroxypyrrolidine (from Angylocalyx boutiqueanus). The biological activity of compound (1) will be reported later.